Dry toner electrostatic printing inks, including laser and xerographic inks, are important and growing contaminants in the area of wastepaper recycling. Traditionally, paper has been printed with water or oil-based inks which were adequately removed by conventional deinking procedures. In these methods, secondary fiber is mechanically pulped and contacted with an aqueous medium containing a surfactant. Ink is separated from pulp fibers as a result of mechanical pulping and the action of the surfactant. The dispersed ink is separated from pulp fibers by such means as washing or flotation.
Conventional deinking processes have shown minimal success in dealing with dry toner electrostatic printing inks, with the necessary chemical and mechanical treatments of the furnish proving to be time consuming and often rendering a furnish which is unacceptable for many applications. The development of a deinking program for office waste contaminated with electrostatic printed copy will make this furnish more amenable to the recycling process.
The ability to recycle office waste will prove commercially advantageous and will have a significant impact on the conservation of virgin fiber resources. Although electrostatic printed waste has not reached the volume of impact printed waste commonly seen in the industry, indications are such that usage of electrostatic print is increasing steadily and that waste copies available to the recycling industry will also increase.
Some deinking systems employ chemical aggregation/densification followed by forward cleaning to remove non-impact inks, and flotation deinking to remove impact inks (i.e., offset) and other contaminants. The chemical nature of many of these deinking products has caused them to act as defoamers in aqueous papermaking systems. A separate flotation aid is thus often added to the flotation cell in order to overcome the defoaming effect of the earlier chemicals.
Furthermore, many aggregation/densification systems use relatively high application dosages in order to provide effective treatment. Existing office waste deinking technology utilizes product dosages of about 0.60%-0.75% on fiber to aggregate and densify the toner particles.